1. Field of Invention
The present invention relates to a flow rate control valve used for a fluid pressure apparatus in various industrial machines and vehicles.
2. Description of Related Art
As a pressure compensation type flow rate control valve capable of maintaining a flow rate constant even if a fluid pressure is varied, one such as disclosed in Japanese Patent Application Laid-open No. 2004-183818 is known. In this flow rate control valve, a control spool is slidably disposed in a cylindrical body, and a spring which resiliently biases the spool in the axial direction is interposed between the body and the spool. An inflow side thereof is a variable orifice whose opening can be varied, and an outflow side thereof is a fixed orifice whose opening cannot be varied.
If the upstream fluid pressure is increased, high pressure fluid flows in and the pressure in a valve chamber is increased, and the spool is displaced against the resilient biasing force of the spring. As a result, the opening of the variable throttle is reduced, the pressure is compensated, and a flow rate of fluid flowing downstream is maintained constant.
A problem of the conventional flow rate control valve is that when an upstream fluid pressure is abruptly increased, the flow rate is overshot. Since time lag exists until the Displacement of the spool will begin after the increase in the upstream fluid pressure, if the upstream pressure is abruptly increased, the opening adjustment of the variable orifice can not catch up and excessive amount of fluid flows temporarily.